There is a known board mounted electrical connector disclosed in U.S. patent application Publication No. 2002/0123254. That electrical connector provides a plurality of pairs of differential signal transmission contact s along with grounding contacts which are positioned adjacent to each pair of the differential signal transmission contacts. The pairs of the differential signal transmission contacts and the grounding contacts are provided in two rows along an engagement portion. The leg portions of the contacts are arranged in three rows at the side of the connector to be mounted onto a circuit board.
The leg portions of the board mounted electrical connector are positioned such that the grounding contacts are arranged in a second row, and the signal contacts are arranged in a first row and a third row. The first row is closest to an engagement surface, and the third row is farthest from the engagement surface. Due to this construction, it is necessary for conductive traces on a circuit board, to extend from the first row to pass through grounding patterns of the second row and signal patterns of the third row. In applications requiring high density arrangement of the leg portions, it is practically impossible to form these signal patterns on a single layer of the circuit board. A multi layer circuit board having the grounding pattern formed at an interior layer of the circuit board and signal patterns formed on an outer layer(s) could be used to address this issue. However, multi layer circuit boards will increase the cost to manufacturer the electrical connector. In addition, in the case that a multi layer circuit board is to be utilized, two layers become necessary to form signal patterns thereon. Therefore, the degree of freedom in circuit board design will be reduced.